Waterfowl and the Issue of Sphincters or Do Ducks Have a Sphincter Muscle?

A friend recently asked me if it is true whether or not ducks (and other birds) have a sphincter muscle. According to one source I use quite often, they do not. I also haven't known anyone who has successfully house trained a pet duck or goose. In this entry I will attempt to solve the puzzle and let you know if your duck or goose does, in fact, have a sphincter muscle. This does not mean, however, that your pet bird can be house trained.

Back in 1989 A. H. Mahdi and J. McLelland called their research "A Morphometric Study of the Rectocoprodeal Sphincter in the Domestic Duck", concluding that there is 'evidence for a sphincter" and that "in the domestic duck, a sphincter muscle, the rectroprodeal sphincter, exists close to the junction of the rectum and coprodeum. Here is a quote from their research:

The caudal part f the ctu in birds opens into the cranial compartment of the cloaca, the coprodeum. There is considerable debate as to whether or not an anatomical boundary exists at the junction of the rectum and coprodeum.

In this same study they go on to report:

Since similar morphometric observations on the innervation of sphincters have previously been made in birds (Mahdi & McLelland, 1988) and mammals (Cai & Gabella, 1984; Vaithilingam et al. 1984) these quantitative data are further support for the existence in this part of the gut of a powerful sphincter. Although the sphincter anatomically belongs entirely to the rectum, its close proximity to the coprodeum suggests that functionally it would be more appropriate to refer to it as a ‘rectocoprodeal’ sphincter.

So far I have located no further studies on this topic. My conclusion is that ducks do have a sphincter, but it operates differently from the sphincters in mammals like ourselves and this is why no one is successful at potty training ducks. If you get a pet duck, expect that it will evacuate (poop) everywhere no matter how much you try to house train it. This is one of the key factors to consider when you decide to take a duck into your home as a pet. There are resources out there to help you, particularly if you have one pet house duck. You can purchase duck diapers which you will need to change frequently.